FES systems have been published in the prior art literature such as U.S. Pat. No. 4,499,900 (Petrofsky et al) and U.S. Pat. No. 4,838,272 (Lieber). One system that has been commercially developed and relates to the Petrofsky teachings is that marketed by Electrologic of America Inc, with a system known as StimMaster Orion, which uses FES as a form of therapeutic treatment. Controlled electrical stimulation currents are passed through electrodes to initiate muscle contractions, for example in the lower extremities of a paralysed patient, thereby causing pedalling of an exercise cycle. The Petrofsky system uses position sensors to measure the position of pedals and these signals are used to control the generation of stimulation signals to the user's electrodes. The aim of these systems is to elicit a constant pre-set velocity of pedalling as a therapeutic treatment for disabled persons, such as paraplegics. In the event that the velocity of cycling does not achieve the desired pedal cadence (preset to 50 rev·min−1), then the apparatus will increase or decrease the stimulation amplitude delivered to muscles to change the speed back to the desired pedal cadence.
Such prior art systems rely solely upon applied stimulation to the limbs to initiate and control the exercise being undertaken. Therefore, should the individual wish to exercise at a greater level or intensity, the amount of stimulation applied to the limbs must be increased to this level to achieve such intensity. The likelihood of over-stimulation of the muscles is therefore greatly increased and the potential of such systems to cause permanent damage to the recipient is high. For this reason such exercise systems have not been widely accepted as therapeutic devices.
The Lieber U.S. Pat. No. 4,838,272 discloses adaptive closed loop electrical stimulation of muscles by a technique including applying electrical stimulation signals to selected muscles at a predetermined frequency, pulse width and amplitude. The work output achieved by the muscles in response to stimulation signals is determined over a period of time, and can be compared with target values. The amount of electrical energy delivered to the muscles by stimulation signals is varied in response to the results in order to maximise the work output of the muscles during a treatment period, this being accomplished by adjusting the frequency or pulse width during stimulation treatment in response to the work output measured.
Such a system also has the problem that should the individual wish to perform high intensity exercise then they are solely reliant on increasing the amount of electrical energy delivered to the muscles. Such an increase can therefore cause over stimulation of the muscles and risks causing permanent damage in much the same manner as the systems described above.
Another known class of exercise machine for therapy purposes, particularly for paraplegics having minimal or no muscle function, is one in which the user is passive and the machine such as a cycle exerciser is motor driven to drive at a selected speed whereby the user's limbs follow and are thus exercised. Such systems, whilst reducing the risk of over stimulation of the muscles and permanent damage associated therewith, are limited in the amount of benefit they can provide with regard to muscle strength and/or cardiorespiratory exercise training.
Further publications related to the present field are U.S. Pat. No. 4,724,842 (Charters), EP 103490 (Wright State University), U.S. Pat. No. 6,267,709 (Jacques et al), U.S. Pat. No. 4,865,315 (Paterson et al), U.S. Pat. No. 4,586,510 A (Glaser et al) and U.S. Pat. No. 4,653,479 A (Maurer).